1. Field of the Invention
The present invention relates to an internal combustion engine which is intended to reduce the noxious content of the exhaust gas, especially, nitrogen oxides (NO.sub.X) and to improve the mileage.
2. Description of the Prior Art
Recently, in an internal combustion engine for automobiles, not only the purification of the exhaust gas but also the improvement in the rate of fuel consumption are required. For these requirements, an EGR (exhaust gas recirculation) and a lean combustion are frequently performed. In order to prevent the combustion fluctuations and the misfire while satisfying both the requirements for the heavy EGR and the lean combustion, it is known that it's preferable to increase the burning velocity.
In order to raise this burning velocity, there have been recently proposed several suction systems, in which a sub-suction path provided separately from a main suction path is designed to inject a gas into a combustion chamber, thereby generating a swirl of the suction gas in the combustion chamber.
However, the suction system provided with such a sub-suction path is in a transient range to the practical use and has much to depend upon the future investigation. In the conventional suction system, indeed, since the intensity of the swirl generated in not sufficient, there arises a limit to the lean combustion and considerable improvement in the rate of fuel consumption cannot be expected, if the heavy EGR is performed while taking preference of measures for the exhaust emission control, especially, the reduction in the NO.sub.X emission.